Top-left: Godhead Pickle Inspector, in Problem Sleuth’s epilogue, fondly regards creation while wearing the Stiller shades that witnessed every event in the universe.
Top-right: Dave is introduced in Homestuck Act 2, wearing Ben Stiller’s shades. MSPA’s legacy carries on.
Bottom-left: Dave in Act 4. I suspect this recurring motif has to do with memory, with events that are best forgotten living on regardless of what happens. (Such as this doomed timeline.)
Bottom-right: Dave in Act 6 Act 6 Act 6. Serenity’s/The Firefly’s appearance during this flash serves, to all characters she/it passes, as a subconscious reminder of all they fight for, all that has come before– gone, but not forgotten. The pre-Retcon timeline (from which the fireflies came) is essentially one massive exploration of this theme.